Highly sensitive polarimetric camera (B-BOP) for the SPICA mission

The Space Infrared telescope for Cosmology and Astrophysics (SPICA) mission has just been selected by the European Space Agency as one of the three candidate missions to be further studied for the medium size mission M5. B-BOP, formerly named POL, is one of the three scientific instruments of SPICA which aims, among other scientific goals, to map the galactic filamentary structures and their associated magnetic fields. With a novel interlaced-shaped design, B-BOP will contain 1344 pixels, operating within a temperature range of 50-100 mK, covering a 2.6 arcmin field of view, and delivering imaging polarimetry in three spectral bands: 100 μm, 200 μm, and 350 μm simultaneously. In this paper, we investigate by numerical simulations the mechanical, electromagnetic, and thermoelectric behaviors of B-BOP detectors and predict for the three bands (i) a sufficient mechanical stability, (ii) a good electromagnetic absorption higher than 95%, (iii) a high response value better than 10¹¹  V/W, and (iv) especially a very low noise equivalent power reaching 1  aW/Hz^1/2 at 50 mK.